1. Field of the Invention
The present invention relates to a magnetic recording medium incorporated within a magnetic disk drive or storage system such as a hard disk drive (HDD). In particular, the invention relates to a method of making a magnetic recording medium comprising a disk-shaped non-magnetic substrate and a magnetic block embedded into the surface of the non-magnetic substrate so as to establish a positional mark.
2. Description of the Prior Art
For example, Japanese Patent Application Laid-open No. 10-83640 discloses a magnetic recording disk or hard disk (HD) comprising a disk-shaped non-magnetic substrate and magnetic blocks or pieces embedded into the surface of the non-magnetic substrate. The magnetic pieces are designed to establish positional marks utilized in the servo control of a read/write head. In process of producing the hard disk, embedment depressions for receiving the respective magnetic pieces are defined on the surface of the non-magnetic substrate. As conventionally known, such a non-magnetic substrate can be represented by a glass wafer, a silicon wafer, an aluminum wafer covered with an NiP lamination, and the like.
As disclosed in the aforementioned Laid-open No.10-83640, a reactive ion etching (RIE) process is usually employed to form the embedment depressions. The RIE process is designed to utilize a photomask so as to transfer the arrangement of the magnetic pieces, namely, a servo pattern, onto a photoresist spreading over the surface of the non-magnetic substrate. As conventionally known, the photomask is subjected to a contact exposure. In this contact exposure, the servo pattern established in the photoresist cannot fully reflect the accuracy of the servo pattern defined in the photomask. The servo pattern in the photoresist suffers from some deviation from the model pattern. In addition, the mass production of the substrate employing the RIE process should include repetition of stages, such as application of the photoresist, exposure and development, etching, and the like, for the individual wafers. It leads to an increased production cost and a deteriorated efficiency of production.
It is accordingly an object of the present invention to provide a method, of making a magnetic recording medium, suitable to mass production at a lower cost in a shorter cycle. It is another object of the present invention to provide a magnetic recording medium capable of realizing the arrangement or pattern of magnetic blocks for positional marks at a higher accuracy, and a method of making the same.
According to a first aspect of the present invention, there is provided a method of making a magnetic recording medium, comprising: forming or molding a disk-shaped non-magnetic substrate with a die, said non-magnetic substrate defining an embedment depression on a surface; and filling the embedment depression with a magnetic material so as to form a magnetic block for a positional mark.
The method of this type enables the production of the non-magnetic substrate suitable to a magnetic recording medium by utilizing the die or mold. As well known, the dimensional accuracy of a molded or resulting product taken out of the die usually depends on the dimensional accuracy of the die. If the arrangement and/or contour of the embedment depression can be defined in the die at a higher dimensional accuracy, it is possible to form the embedment depression on the surface of the non-magnetic substrate at a higher accuracy as expected. The magnetic block is allowed to reliably reflect the accuracy of the die as designed.
Utilization of the die in the method enables mass production of the non-magnetic substrate with a single die. For example, hundreds of thousands of the non-magnetic substrates may share the production cost of the die. Even when the die suffers from a higher production cost, it is possible to reduce the cost for the individual non-magnetic substrates by sharing. A cheaper magnetic recording disk can be obtained.
Moreover, the above-described method enables the formation of the embedment depression during molding, namely, within the die. It is not necessary to prepare relatively expensive equipment or plants for achieving application of a photoresist, exposure and development, etching, and the like, in defining the embedment depression on the surface of the non-magnetic substrate. As compared with the case where reactive ion etching (RIE) is employed to form the depression, for example, the production cost per an individual non-magnetic substrate can be reduced to the utmost. In addition, employment of the above-described method enables elimination of processes such as application of a photoresist, exposure and development, and etching for individual non-magnetic substrates, so that the efficiency of the production can be improved. Great numbers of the non-magnetic recording disks can be produced in a shorter cycle.
The method of making may further comprise: pouring a fluid non-magnetic material into the die; and forming a sinter of the non-magnetic substrate out of the fluid non-magnetic material within the die. This method allows the resulting sinter to reliably reflect the shape of a cavity or hollow space defined within the die. The non-magnetic substrates of the identical shape or form can constantly be obtained unless the die suffers from deformation.
Here, a polycarbodiimide may be employed as the fluid non-magnetic material. Dehydration of the polycarbodiimide enables establishment of the sinter corresponding to a disk-shaped non-magnetic substrate containing carbon. The non-magnetic substrate of this type exhibits a sufficient heat resisting property during the subsequent formation of a seed crystal layer, a surface magnetic layer and a protection layer. For example, the non-magnetic substrate may suffer from a higher temperature smaller than 400 degrees Celsius during sputtering. Alternatively, the fluid non-magnetic material may be a gel of (Bi2O3)20(SiO2)80 containing a polyethylene glycol of molecular weight ranging 200 to 600, for example. Dehydration of the gel serves to provide a sintered non-magnetic substrate containing SiO2. Likewise, the non-magnetic substrate of this type is allowed to have a sufficient heat resisting property during the subsequent formation of a seed crystal layer, a surface magnetic layer and a protection layer.
It is preferable that the aforementioned magnetic block is magnetized along the vertical direction perpendicular to the surface of the non-magnetic substrate. In this case, the magnetic recording medium may be inserted into a magnetic field including a magnetic flux running in a specific single direction. The magnetic field of this type allows all the magnetic blocks, embedded in the magnetic recording disk, to simultaneously be magnetized in the vertical direction. The efficiency of the production can still further be improved. A coil of a size enough to contain the overall magnetic recording medium within its inner space may contribute to establishment of the magnetic field of the above-described type based on electromagnetic induction.
According to a second aspect of the present invention, there is provided a magnetic recording medium comprising: a disk-shaped non-magnetic substrate; a depression defining an embedment space opened at a surface of the non-magnetic substrate; and a magnetic block embedded within the embedment space, said magnetic block magnetized along a vertical direction perpendicular to the surface of the non-magnetic substrate.
The magnetic recording medium enables a reliable leakage of a magnetic field out of the magnetic block embedded in the non-magnetic substrate. The magnetic field of the magnetic block can be utilized in a tracking servo control of a corresponding read/write head, for example. Moreover, the magnetization of the magnetic block or blocks can be achieved in a facilitated manner as described above.
The magnetic block may include, in order to establish the vertical magnetization, a first metallic film containing at least one of Pt, Pd and Au, and a second metallic film superposed on the first metallic film. The second metallic film may contain at least Co. Alternatively, the magnetic block may contain at least Fe and either of Pt or Pd. Otherwise, the magnetic block may include an alloy film containing Co, Ni and P.
According to a third aspect of the present invention, there is provided a die for making a substrate of a magnetic recording medium, comprising an interior surface defining a hollow space corresponding to a shape of the substrate. The die of this type greatly contributes to achievement of the aforementioned method of making suitable to mass production of the non-magnetic substrates for the magnetic recording mediums. It is possible to reliably reduce the cost for the individual non-magnetic substrates. A cheaper magnetic recording disk can be obtained. In this case, the interior surface of the die may include a bump corresponding to the aforementioned embedment depression defined on the non-magnetic substrate.